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Summer 2010 Vol. 10 Number 2

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EYE on the SKY

Artist’s concept of disintegrating asteroid, courtesy NASA Jet Propulsion Laboratory

Earth is regularly bombarded by objects from space -- most of them small meteorites and dust that burn up harmlessly before striking the planet's surface. But once in a great while a larger intruder appears. In 1908, an object exploded in the atmosphere above Siberia, severely damaging a forest of over 2,000 square kilometers. And the dinosaurs may well owe their demise to an asteroid that struck the Yucatan peninsula 65 million years ago, leaving behind a crater more than 180 kilometers in diameter.

How can we know if another object of such dangerous potential is on the way, and is there anything we can do about it? These and other questions about near-Earth objects (NEOs) were explored in a recent report from the National Research Council, which recommended that government and scientists do more to identify cosmic objects that could be dangerous.

NASA is close to achieving its congressionally mandated target for spotting the largest objects -- those at least one kilometer in diameter, which could cause destruction on a global scale, the report notes. But the agency cannot complete its second assignment -- by 2020 to discover 90 percent of objects that are at least 140 meters in diameter -- because it lacks the funds to do so. NASA could meet this goal soon after the original deadline if provided funds to field either a mission using a space-based telescope or a slower-but-cheaper survey using a ground-based telescope.

Policymakers and scientists also should set their sights on smaller objects, the report says. Recent research suggests that NEOs as small as 30 to 50 meters in diameter can be destructive. The size of the Siberian meteor was probably in that category, and if such an object fell over New York City, hundreds of thousands of deaths might result.

The report also explores ways to defend against an NEO if we find one on a collision course with Earth. These range from civil defense -- which includes evacuations and seeking shelter from an impact --to trying to send the object off course with a nuclear explosion. Other options for altering the NEO's path include flying a spacecraft directly into the object, or pushing or pulling it using gravity. While these methods are conceptually valid, they are also relatively new and immature, the report says. It recommends that the U.S. create a new research program to better assess the NEO impact hazard and ways to lessen it. And the nation should take the lead in organizing an international entity to develop a detailed plan for dealing with the threat. --  Sara Frueh

Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies. Committee to Review Near-Earth Object Surveys and Hazard Mitigation Strategies, Space Studies Board and Aeronautics and Space Engineering Board, Division on Engineering and Physical Sciences (2010, 152 pp.; ISBN 0-309-14968-1; available from the National Academies Press, tel. 1-800-624-6242; $36.50 plus $5.00 shipping for single copies).

The committee was chaired by Irwin I. Shapiro, former director, Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. The study was funded by NASA.

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Copyright 2010 by the National Academy of Sciences